Continuous strip pickling



Nov. 16, 1943- s. J. DIsHAuzl CONTINUOUS STRIP PICKLING Filed July 24, 1941 Patented Nov. 16, 1943 CONTINUOUS STRIP PICKLING Steve J. Dishauti, Hollidays Cove, 1V. Va., assignor to National Steel Corporation, a. corporation of Delaware Application July 24, 1941, Serial No. 40t,902

5 Claims. (Cl. 148-8) This invention relates to an improved. continuous pickling method and apparatus for strip metal to attain higher speed of the strip while y maintaining satisfactory pickling.

Continuous pickling of strip metal is old. In the systems of the prior art the strip was passed through a series oftanks containing pickling solution, the process being stopped When the pickling solution was to be renewed. United States Patent No. 2,166,583 to Critten discloses an improved process in which pickling of the strip continues while one tank of pickling solution is being renewed. In order to accomplish tion in this tank can perform a proportion ofA the pickling comparable to that performed in each of the following tanks containing fresher solution. On the other hand, a fresh pickling solution in this tank would attack the strip with v such vigor that the solution would soon be spent.

This would put no burden on the subsequent tanks at first but would throw the burden on l these tanks as the solution in the rst tank be- 'came spent.

The solution in the Second tank would then heavily attack themetal after the solution in the first tank was spent. Recharging the first tank with fresh pickling solution would again cause the heavy reaction to be transferred to this tank. When the tanks subsequent to the first tank contained .fresh solution, the' heavy reaction in the first tank would result in overpickling by the fresh solution in the subsequent tanks. When the reaction in the rst tank fell oli sharply and the solution in the subsequent tanks was partially depleted, underpickling of the strip would result. Thus a sharp rise and fall of the pickling action would follow replenishing-and depletion of the solution in the first tank.

To avoid this situation I have evolved a pickling method in which a partially spent pickling solution is charged to the first tank and the condition of the solution in this tank governs the replenishing of the subsequent tanks. The extent of the reaction in the rst tank is thus mainless effect.

tained at a reduced level and the effect of using new pickling solution is minimized on the operation of the pickling line by such solution being used only in the subsequent tanks where it has A further result of this manner of operation is that the minimum speed of the strip is greatly increased. With a plurality of tanks in use and the condition of the solution in the first tank such as necessitatesdumping, the speed of the strip is reduced as this tank is dumped. Since the waste solutionV being dumped was hav- 'ing a very slight pickling a-ction on the strip, the

reduction in speed' of the strip at this point `need be slight. With a solution which is only partially spent being transferred from a subsequent tank to the rst tank, no further reduction in the speed of the strip is necessary. While the subsequent tank is being replenished the speed of the strip can be gradually raised to the maximum for obtaining satisfactory pickling. Thus, contrary to the systems of the prior art, at no timeis a minimum number of tanks being used with one of the tanks having a spent solution therein. l

'In order to increase the pickling action of the partially spent solution in the rst tank to a. maximum, I have devised a system for circulating the solution using the heating medium, Due

to the strip manufacturing process resulting'in I 'inducing a stream of the pickling solution to -irnpinge upon the edge4 of the strip along its path through the tank, I have raised` the action,

of the pickling solution at that point to a maximum.

An important object of the present invention is the provision of a method of pickling continuous strip at a high rate of speed and with a minimum of speed reduction during recharging of the pickling solution.

Another important object of the present invention is the provision of apparatus for increasing the action of a pickling solution o'n the edges of4 part of the present disclosure and in which like reference numerals designate like parts,

Figure 1 is a side elevation, partially in section,

of apparatus capable of carrying out the method of my invention.

Figure 2 is a cross-section taken on the line 2-2 of Figure 1, showing the pickling solution circulation system.

Figure 3 is a plan view of the tank of Figure 2.

Reference numerals Ill, II, I2 and I3 indicate pickling solution tanks arranged in series to form a pickling line. Tank I is situated at a lower levelthan the others to make possible gravitational ilow of the pickling solution being transferred. Strip to'be pickled is fed by power driven rolls I4 over guide roll I5 into tank I 0. The

.strip passes under weighted rolls I6 located at each end of tank I0 and designed to maintain the strip under the surface of.pickling solution I'I. Strip I4 emerges from tank Il) and passes over guide roll I1' to tank II where it passes under weighted rolls I8 similar to roll I6 through pickling solution I9. Strip I4 emerges fromv tank I I and goes over guide roll 2|! into tank I2 wherein it is maintained under the surface of pickling solution 2| by weighted rolls 22. Strip I4 emerges from tank I2. goes over guide roller 23 and enters tank I3 wherein it is maintained under the surface of pickling solution 24 by Weighted rollers 25. Strip I4 emerges from tank I3 and passes under guide roll 26 to further treatment and coiling not shown.. Obviously rolls I6, I8, 22 and 25 could be omitted since gravity would cause thestrip to-hang in-catenaryform.betweenthe guide rolls I5, Il', 20, 23 and 26, thus to be guided through each tank.

resistant lining 30 is bonded to the walls and bottom of tank lll. A protective lining 3| formed of acid resistant refractory bricks or the like is placed on the,.inside of the lining 30. Submerged in pickling solution I1 is the strip metal I4. Steam is used to maintain the pickling solution at the required temperature and steam supply pipes are shown at 32 entering the tank. These steam supply pipes connect with headers 33 which extend along the length of the tank adjacent the side walls and resting on the bottom. Each header 33 has a plurality of jets 34 which are directed at an angle of about 45 so that a stream of steam emitted therefrom will impinge upon the strip metal at its edge. Brackets 35 support header 33 against rotation due to the weight of the jets and the reaction of the stream of steam.A Although this structure is shown applied to tank I0, the same heating and agitating system can be used in the other tanks.

With the system operating and the metal strip.

travelling through all the tanks, the action of the acid, preferably sulphuric acid, results in the formation of iron sulphate in the pickling solution. Since the oxide and other impurities on the metal strip are heaviest in tank I, the action of the acid is greatest here. There would, therefore, be a more rapid production of iron sulphate in this tank where the initial pickling solution in each tank is the same. The operator of the pickling line observes the increase of iron sulphate in the pickling solution of each tank together with the reduction in concentration of acid. The proper concentration of acid is maintained in each tank, including the ilrst tank, by the addition of acid. It has been found that an acid concentration of 25 to 30% in the rst and second tanks, and somewhat lower in the others is satisfactory wh'en treating low carbon hot rolled strip steel. The acidv concentration in the rst tank may be somewhat higher or may be substantially equal to that in the second tank. When the concentration of iron sulphate in the first tank exceeds about 30%, preparations may be initiated for dumping the solution. After this point is reached no more acid is added to the solution in the first tank so the acid content will approach 15 to 20% at time of dumping. Depending upon the extent of pickling desired and the speed ofthe strip metal, concentration of iron sulphate in this tank may be allowed to mount over 35%. When the iron sulphate concentrtaion has reached the desired maximum point, the operator proceeds to dump the solution from this tank. Despite the high concentration of iron sulphate in the solution being dumped, some pickling action is present; therefore, with this tank emptying, the overall pickling action of the line is being reduced and the strip metal speed must be reduced slightly so that the increased pickling time will make up for the pickling action lost in tank l. The operator then transfers the pickling solution from one of the subsequent tanks to the first tank, the subsequent tank chosen being that having the highest concentration of iron sulphate in the solution. A new batch of pickling solution is then prepared in the subsequent tank from which the solution was transferred and the speed of the strip metal is highest iron sulphate concentration is chosen to be transferred to the first tank because, as'meneY tioned above, the action of the acid on the strip metal is considerably greater in this tank. Placing partially spent solution'in this tank reduces this action somewhat and at the same time results in the most eicient use of the partially spent solution. The partially spent solution fortified by the addition of acid may be used for the major fraction of a day or more before the metal content becomes too high. Generally speaking, with the low carbon strip metal and a speed of the strip between 350 and 400 feet per minute, depending on the Width of the strip, the concentration of iron sulphate in the first tank is allowed to reach 32 to 40% although a few percent one way or the other is not critical. While dumping the first tank the speed may be reduced to about 250 feet per minute. In such operations the subsequent tank having next highest concentration of iron sulphate will usually run between 10% and 20% iron sulphate. With strip 36 inches wide, I have found a speed of 375 feet per minute 55 satisfactory and an iron sulphate concentration of about 38% the maximum desirable.

In order to obtain the most efiicient action of the partially spent pickling solution in tank I, I have devised the combined heating and agitating system which makes possible maximum speed of the strip metal with satisfactory pickling. This heating system maintains the solution in all the tanks at about 215 F. Headers 33 and jets 34 are arranged so that the stream of heating steam ejected into the pickling solution causes a stream of solution and steam to impinge on the edge portions of the strip metal. It is these portions that are not properly pickled when satisfactory pick-V simultaneouslyincreased.. .'Ihesolution .with 4the, ,V

Due to the high temperature used in the present process and the high concentration of iron is believed that the rapidly moving stream of solution and steam caused by jets 34 acts directly on this salt tolbrush the same of the surface of the strip to eliminate this difficulty.

I claim:

1. In a method of pickling continuous strip metal wherein the same is passed through a plu- L rality of tanks in succession, the number of tanks being greater than the minimum number necessary under normal operating conditions for satisfactory pickling at minimum desirable speed of the strip metal, the steps comprising maintaining an acid pickling solution having a metal con- As the the strip metal, the steps comprising maintaining an acid pickling solution having a metal content less than an allowable maximum in al1 the tanks,

passing the strip metal through the tanks at a tent less than an allowable maximum in`all the tanks, dumping the first tank relative to movement of the strip metal when the metal content of the pickling solution therein reaches the allowable maximum, transferring the pickling solution from asubsequent tank relative to movement of the strip metal to the first tank, said subsequent tank being the one having the highest metal content at the time, replenishing the subsequent tank with fresh pickling solution, and maintaining the acid concentration of the first tank at least as high as that of the subsequent tanks until the metal content of the pickling solution in the rst tank reaches a point near the allowable maximum.

2. In a method of pickling continuous strip metal wherein the same is passed through a plurality of tanks in succession, the number of tanks being greater than the minimum number necessary under normal operating conditions for sat-'` isfactory pickling at minimum desirable speed cf the strip metal, the steps comprising maintaining an acid pickling solution having a metal content less than an allowable maximum'in all the tanks, dumping the first tank relative to movement of the strip metal when the metal content of the pickling solution therein reaches the allowable maximum, transferring the pickling solution from `a subsequent tank relative to movement of the strip metal to the first tank, replenishing the subsequent tank with fresh pickling solution, and maintaining the first two tanks about the same in acid concentration and higher than the subsequent ,tanks relative to movement of the strip metal until the metal content of the pickling sospeed above the minimum speed, dumping the first Ytank relative to movement of the strip metal when the metal content of the pickling solution therein reaches the allowable. maximum, reducing the speed of the metal strip to the minimum, transferring to the rst tank the pickling solution from the subsequent tank having the next highest metal content, replenishing the subsequent tank with fresh pickling solution, raising the speed of the f strip metal above the minimum, and maintaining the acid concentration of the first tank at least as high as that of the subsequent tanks until the metal content of the pickling solution in the first tank reaches a point near the allowable maximum.

4. In a method of pickling continuous strip metal wherein the same is passed through a plurality of tanks in succession, the number of tanks being greater than the minimum number necessary under normal operating conditions for satisfactory pickling at minimum desirable speed of the strip metal, the steps comprising maintaining an acid pickling solution having a metal content less than an allowable maximum in al1 the tanks, passing the strip metal through the tanks at a speed above the minimum speed, dumping the rst tank relative to movement of the strip metal when the metal content of the pickling solution therein reaches the allowable maximum; reducing the speed of the metal strip to the minimum, transferring to the first tank the pickling solution from the subsequent tank having the next highest metal content,jreplenishing the subsequent tank with fresh pickling solution, raising the speed of the strip metal above the minimum, and maintaining the acid concentration of the first tank higher than that of the subsequent tanks until the metal content' of the pickling solution in the first tank reaches a point near the allowable maximum.

5. In a method of pickling continuous strip metal wherein the same is passed through a plurality of tanks in succession, the number of tanks being greater than the minimum number neceslution in the rst tank reaches a point near the allowable maximum.

3. In a method of pickling continuous strip metal wherein the same is passed through a plurality of tanks in succession, the number of tanks being greater than the minimum number neces'- sary under normal operating conditions for satisfactory pickling at minimum desirable speed of sary under normal operating conditions-for satisfactory pickling at minimum desirable speed of 50` the strip metal, the steps'comprising maintaining an acid pickling solution having a metal content less than an allowable maximum in all the tanks, dumping the first tank relative to .movement of the strip metal when the metal content of the pickling solution therein reaches the allowable maximum, transferring to the first tank the pickling solution from one of the subsequent tanks relative to movement of the strip metal, said one of thesubsequent tanks being the one having the highest metal content at the time, the metal content being not substantially greater than onehalf the allowable maximum, replenishing said one of the subsequent tanks with fresh pickling solution, and maintaining the acid concentration of the first tank at least as high as that of the subsequent tanks until the metal content of the pickling solution in the first tank reaches a point near the allowable maximum.

STEVE J. DISHAUZI. 

